PV arrays are generally built by arranging multiple individual PV cells into a larger panel. These cells can either be connected in series or in parallel or a combination of both. Larger arrays may also include multiple panels. One single PV cell has only one unambiguous optimum operating point for a given rate of insolation and temperature. If all cells in a PV array are identical and subjected to equal insolation and temperature conditions, the array as a whole will also have only one single optimum operating point. The total output power at this point will be the sum of the power optima of all individual cells. If however the individual cells do not have completely identical properties due to production tolerances or aging, or if not all cells experience equal insolation due to fouling, damage or partial shading, the total output power will be less than the sum of the individual optima. The maximum achievable output power of such an array will be sub-optimal. It may even have multiple local maxima in its power curve, which makes finding the true optimum difficult.
When connecting panels in parallel the voltage across their terminals will be equal by definition. If the panels are not identical or if they experience different insolation or temperature conditions, the panels will have different voltages where their maximum power points occur. This implies that it will be impossible to find a load that will cause each panel to work at its optimum operating point. Analogues, when connecting panels in series their current will be forced equal. This also prevents each panel to work at its maximum power point (MPP) if they are not completely identical or subjected to different conditions. A maximum power point tracker (MPPT) connected to a PV array having multiple panels can at best reach an average optimum point of operation, where none of the individual panels may work at their MPP.
Up to now finding the peak in the power curve only of PV panels has been considered. For small PV panels this locking to the nearest peak in the power curve from the current point of operation is adequate since these typically exhibit one single maximum power point. Large PV arrays however, may show multiple power peaks and valleys if the individual PV cells are ill matched or exposed to unequal lighting conditions or temperature. Without further measures a MPPT will lock to one of these peaks, which may or may not be the peak with the highest magnitude.
In other applications, a single MPPT is used for the entire PV array. These MPPTs need an elaborate way of control in order to handle the potential presence of multiple peaks in the power curve.
To address the needs in the art, maximum power point tracking performed locally for each panel is provided. The output power of these individual MPPTs can then be summed and fed to the load.